Rigid polyisocyanurate/polyurethane (PIR) foams are widely known and are used in numerous industries. PIR foams are hybrid structures having both groups: urethane groups (resulting from the reaction of —NCO groups of isocyanates with the hydroxyl groups of polyols) and isocyanurate rings, derived from the trimerisation of an excess of —NCO groups against the hydroxyl groups (isocyanate index of greater than 100, for example, 180-600). Trimerisation of —NCO groups is typically catalyzed by special catalysts, such as tris(dimethylaminomethyl) phenol, potassium acetate and other catalysts. The highly crosslinked structure of the PIR foams is derived from the isocyanurate rings generated by the trimerisation of the excess of —NCO groups.
PIR foams are continuously subjected to increased regulations with respect to flame retardant traits and reduced smoke generation. Flame retardant traits and reduced smoke generation are typically improved because of the presence of isocyanurate rings. However, existing trimerisation catalyst systems for producing such isocyanurate rings tend to be active only at high temperatures, which is typical within the core zone of PIR foams. Therefore, the existing trimerisation catalyst systems tend to facilitate the formation of isocyanurate rings mainly in the core zone of the PIR foams. Although the use of existing trimerisation catalyst systems improves the flame retardant and smoke generation traits of the core zone of PIR foams, there is still a need to further improve such properties within the outer zones of such PIR foams. The instant invention facilaites the formation of isocyanurate rings within the outer zones of such PIR foams, and as a result facilitating the improvement of flame retardant and smoke generation traits of the outer zones of PIR foams. The instant invention facilitates and increases the trimerisation of the isocyanurate rings in the outer zones of PIR foams by requiring lower activation temperatures. The instant invention may further provide improved bonding properties, for example, in lamination processes, that is, tensile bond strength of double steel facers of PIR foam panels.